PV System Rapid Shutdown: Page 3 of 4


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Like all microinverters, this Enphase S230 offers RSD capability by default.
SolarEdge offers a fully RSD-compliant solution with its Power Optimizers (DC-to-DC converters), which are designed to be installed with SolarEdge inverters.
This ABB low-profile RSD pass-through box fits behind a module, connecting to the series string positive and negative wires via the locking connector (H4) input leads. The output is connected to the output circuit routed to an ABB UNO or PVI inverter. This RSD solution is offered in one- or two-string models.
The Fronius Rapid Shutdown Box works with single or multistring arrays and with various Fronius inverters.
The Ginlong Solis RSD is offered in one- and two-string models, and connects directly to the PV strings via MC4 cables.
SMA’s TL inverter line offers limited backup power during the daytime with its SPS feature. The RSD solution shown here uses a remote switch, instead of loss of utility power, to initiate shutdown.
The Yaskawa-Solectria Solar Rapid Shutdown combiner can accommodate up to four input series strings and is compatible with its PVI transformerless inverter line.
The OutBack Power ICS Plus Combiner and RSI Initiator can work in grid-tied and/or battery-based systems, and are not dependent on using OutBack inverters.
The Bentek Rapid Shutdown system offers two- and three-string options for grid-tied inverters. The rapid shutdown controller shown here is used to initiate shutdown and is installed in an accessible location.
The Innovative Solar RSD is available as a SolaDeck flashed rooftop combiner or in a nonflashed, nonmetallic version. (An eight-string input version is also available.)
The MidNite Solar Rapid Shutdown system, which can be used in battery-based and grid-tied systems, includes the Birdhouse (above) that controls disconnecting combiner boxes (right) and remote trip breakers (not shown).
The Phoenix Contact SolarCheck RSD offers module-level rapid shutdown.
The Solar BOS line provides rapid shutdown of up to eight series strings, and works with grid-tied string inverters.

Battery-based inverters have no DC input capacitors, so that eliminates one RSD (unless it’s an AC-coupled system, see below). However, charge controllers may have capacitors that may require RSDs on the incoming PV DC circuit conductors.

If battery-to-inverter conductors are more than 5 feet long, an RSD method may need to be included to activate their shutdown. NEC 690.71(H) also requires a disconnecting means at the battery bank when its conductors are longer than 5 feet. Because these conductors are in a building, a simple DC disconnect at the battery bank isn’t sufficient—emergency responders need to be able to activate shutdown from an accessible location (i.e., outside of the building), so the RSD method will need to be remotely activated. Since the battery bank powers the inverter and any DC load, once that battery RSD device (and the PV DC circuit RSD) is activated, all other circuits (DC load circuits and inverter AC output circuits) are also shut down, so system shutdown is complete.

Grid-tied with battery backup systems are designed so that, during a utility outage, a critical load subpanel (and in some cases the whole house) will still energize loads from the inverter output, which is powered by the battery bank. Unlike batteryless grid-tied systems, the loss of utility AC power can’t serve to initiate shutdown of this AC circuit—this would render the backup battery bank useless during a utility outage. An RSD initiator for this system must be independent of utility power.

Even if batteries are installed within 5 feet of the inverter, a solution for controlling the backed-up AC circuits may need to be implemented per 690.12. A remotely activated switch or circuit breaker in the battery circuit or in the inverter-output circuit will suffice. Either of these options will shut down circuits that would otherwise remain energized without utility power.

AC-coupled battery-based systems include both batteryless grid-tied inverters and battery-based inverters. In an outage, the battery-based inverter “tricks” the grid-tied inverters into thinking the grid is still present. This keeps the grid-tied inverters producing power, which is used by the critical loads and the battery-based inverter to charge the battery bank. And while these systems require a change in thinking about 690.12, generally they shouldn’t require more RSD devices then a standard battery-based system. For example, an AC-coupled system with an array utilizing microinverters now cannot depend on loss of grid power to initiate rapid shutdown for the PV array. However, since the battery-based inverter relies on the battery bank power to function, a remotely activated DC battery switch or an AC switch that is required to shut down the battery-based inverter output will also automatically shut down the microinverters’ output. 

What’s Ahead: The 2017 NEC & RSD Requirements

Many changes to the 2017 NEC will affect how PV systems need to comply with RSD requirements. In section 690.1, the NEC redefines the conductors considered to be part of the “PV system” as only those associated with the PV array and the output of a batteryless inverter. Battery-to-inverter circuits, DC loads circuits, and battery–based inverter AC output circuits are no longer included. This eliminates RSD requirements for those circuits, making compliance less complicated for battery-based systems.

Comments (5)

Gary Butt's picture

We have RSD controls in some our solar sites and there is still a problem even when you engage the RSD button.
We had a fire on one of our roof top solar sites. The fire dept. wanted the power de-energized from the solar panels. We engaged our RSD button and it opened the inverter. All it did is break parallel between the A/C power source and the D/C power. The wire from solar panels back to the inverter was still energized and A/C to the inverter is still energized. This didn't de-energized the D/C power on the roof top for the fireman to put out the fire. The panels and wire just burned.

Xriva18707's picture

FYI Many recreational vehicles RV have solar panels. But YouTube reviews of these systems do not show 'shutdown' systems.

Edward-Dijeau's picture

The problem is, to be at 30 volts or less, each solar panel must be an 18 volt Solar panel and must be under 240 watts in output from the roof to the inverter or solar charge controler to be exempt from this RSD rule. Most micro inverters, that have UL approval today, need over 30 volts to opperate and the output, if kept on the roof, becomes a nominal 240 volts and should be in electrical raceway. Even if the 240 volts is cut, the 36 volt or higher output is still up at the panel. The only safe way to bring down power without a raceway is to have 18 volt panels with each panel fed separatly down to any converter, inverter, charge controler with no backfeed from other solar panels. Using Double pole, double throw relays, one for each panel. with the common terminal points going one to positive and the other to negative and the normally open cantact termanals connected to the micro inverter and the normally closed contact terminals connected to a charge controler for a back up battery system all using 12 or 24 volt coils and control with control voltage comming through contacts from a Master Control Relay from the Utility incomming power on each phase, can you run a system that would not require a RSD. Most older PV systems could fry a Fireman, even with the PV diconect at thr meter turned off because the DC voltage is still present, on the roof, in open conductors under every panel. The industry wanted to sell their epecialty cables and connectors to fly by night, not licenced installers to instal with "Plug and Play" rather than have the "Solar Panel Junktion Box" fed with real flecable conduit requiring Licenced Inside Wiremen hired by C-10 Electrical Contractors. If all the wiring, on the roof, was in conduit or raceway from the Solar panel junktion Box all the way to the electrical invertes, disconects and Main Electrical panel, both AC and DC, there would be no need for the RDS instalation or retrofit.

randy dunton_2's picture

module level electronics need to be kept as simple as possible in order for cost & longevity to have a chance of succeeding. Furthermore proprietary systems will always lack future proof assurance; will parts be available 5-10 years down the road? Helios Focus has developed a simple module level rapid shutdown switch for module manufacturers, which can be cost effectively licensed and implemented to adhere to NEC 2017 rapid shutdown. This technology was developed in 2009 and since then tested in the Arizona desert heat.

Edward-Dijeau's picture

If the Solar panel Junction Box had an input cable that would not let any power "out" of the Solare Panel unless a 12 or 24 volt signal was detected at the input but would just shunt the panel to a closed loop circuit to protect the Solar Panel's Life expectancy, you would have a safe panel at any desired voltage. This would work for new panels with the built in system. However, if conected to older panels within the required footage BEFORE any micro inverter or series connection, retrofitting would cost as much in labor as the new panel instalation because you would need to run another series of wires to every panel, break apart existing connction to install the device, reconect all the wires and have a Master control relay and low voltage power sorce to fire them. There is also the problem of older code instaltions grandfathered in and when a property is sold, would the upgrade need to be made before the NEW owner took up residance? Would the old owner just chose ro remove the solar before sale rather than pay for a retrofit? If a residential Solar System does not have the upgrade and shut down, could a fire department refuse to go up on a roof and put out a fire on an older Solar systems even with the required AC disconect? I think the older 25 year life expectancy panels will be replaced at the end of life with more efficient, safer solar panel systems, but, like you said, the system developed in 2009 still hase not been made commercialy available because the 2017 codes have not forced the industry to become safer. It took 50 years before the "Grounding 3 wire" receptical replaced the 2 wire neutral grounded keyed receptical so how long will it take for Solar Panels to become safer?

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